Variant CJD was first identified in 1996 in the U.K., and the majority of the 220 cases reported worldwide have been in the U.K. and France. In fact, the CDC believes that each of the four U.S. infections have originated while patients have been traveling abroad. There is no treatment for the disease, and it has an extremely long incubation period. Most patients don't show symptoms—which include neurological signs like unsteadiness, difficulty walking, and involuntary movements—for years, so the full human effect of the disease is still unknown.

However, Europe launched a massive eradication program in the mid-90s, including banning the practice of grinding up cattle bone meal into cattle feed (it's thought that cows who ate the remains of other sick cows that had been processed into protein supplements have contracted Mad cow disease that way) and culling all suspect cattle populations, and the number of cases diagnosed has dropped to fewer than five per year. The U.S. also has a number of safety procedures in place to guard against the disease in U.S.-raised cattle, including testing more than 40,000 dead cattle per year for the disease to identify and isolate vulnerable populations. Because a small amount of evidence suggests that the disease may also be transmitted through humans via transfusion, U.S. citizens who have lived five or more years in Europe since 1980 aren't eligible to donate blood, according to the American Red Cross.

Ultimately, U.S. health officials conclude that this is not a public health threat. Still, this might be a good excuse to stick with salad and limit your beef consumption the next time you travel overseas.